In oracle application framework page the OAF DefaultSingleColumn region was used to hold items in a single column. Prompt of items will be right justified and the input fields will be left justified. But it was not fulfilling the Oracle BLAF (Browser Look and Feel) UI requirement/guidelines.
Hence, it is deprecated and messageComponentLayout should be used for better serving the purpose of placing items in OAF page along with header region which is called before messageComponentLayout in the OAF page.
Along with DefaultSingleColumn layout, there was one more region known as DefaultDoubleColumn layout was present.
DefaultDoubleColumn severs the requirement of placing items in two columns; it is also deprecated due to the same reason of not serving the purpose of Oracle BLAF UI.
Corresponding web bean: OADefaultSingleColumnBean (deprecated)